1. Field of the Invention
The invention relates to the field of implantable cardiac stimulation devices and to identifying patients exhibiting electro-mechanical dysynchrony.
2. Description of the Related Art
Numerous patients suffer from disease conditions that affect their cardiac performance. For example, diseased myocardium generally reduces the mechanical contractile capabilities of the heart. Impaired conduction and/or abnormalities in intrinsic activation can result in inappropriate/impaired stimulation of the cardiac tissue. Damaged valves can limit the sealing capabilities of the heart thereby reducing capacity for normal filling and/or emptying. Dysynchrony in activity among the multiple cardiac chambers also impairs pumping effectiveness.
A variety of implantable cardiac stimulation devices have been developed to provide therapy for at least certain patients suffering impaired cardiac function. Implantable cardiac stimulation devices generally include an implantable stimulation pulse generator and a microprocessor based controller regulating operation of the device. Implantable cardiac stimulation devices also typically include one or more implantable leads which are configured for implantation to extend adjacent the patient's heart. The implantable leads typically include one or more electrodes. The electrodes can be configured for dedicated sensing or for delivery of stimulation or can be configured for combined sensing and stimulation delivery functions. The implantable devices are generally adapted to automatically sense the patient's physiologic status and automatically generate and deliver therapeutic stimulation for observed cardiac abnormalities.
The implantable devices available range in complexity and modes of therapy delivery, for example the particular chamber(s) of the heart which receive therapeutic stimulation. An appropriate configuration and programming of the device is selected depending on clinical evaluations of the individual needs of the patient. Thus, an implantable cardiac stimulation device and corresponding implantable sensing/stimulation lead(s) are configured and operation is programmed for the individual needs of each patient and their individual conditions.
For example, bradycardia pacing devices are adapted to provide therapeutic pacing stimulation to counteract slow arrhythmias. Implantable cardioverter/defibrillators (ICDs) are adapted to provide therapy for tachycardia/fibrillation arrhythmias. Implantable devices can also be configured to provide anti-tachycardia pacing therapy to overdrive pace the heart to treat certain tachycardias.
Multi-chamber pacing can offer significant benefits to certain arrhythmic patients. Bi-ventricular (or Bi-V) pacing is one particular variation of multi-chamber pacing that refers to pacing both the right and left ventricles as indicated. By providing paced control of both ventricles, bi-ventricular pacing can help restore synchrony between the ventricles and increase the overall pumping efficiency of the heart. Such therapy is also frequently referred to as cardiac resynchronization therapy (CRT) as such therapy can be adapted to improve right-left synchronization of ventricular activity.
Multi-chamber pacing is one of the more complicated and expensive therapies available via implantable cardiac stimulation devices. In the particular example of bi-ventricular pacing, as the left ventricle (LV) provides the most energetic contractions of the heart chambers and placing foreign objects inside the LV presents serious risks, implanting stimulation leads into effective contact with the left ventricle is a challenging procedure both for the designers of the implantable device and the physician performing the implantation. Thus, bi-ventricular pacing, while offering significant benefits to certain patients, is also relatively expensive to implement and involves a more complicated and potentially more risky implantation procedure than other implantable device configurations. It will be appreciated that this more complex and expensive therapy is generally reserved for patients for whom a clear potential benefit can be demonstrated.
However, at least certain patients who are not provided with a bi-ventricular-capable device, for example patients provided with a bradycardia pacer or an ICD, may experience a change in their condition such that they may benefit from the more complex bi-ventricular-capable device. For example, at least certain patients provided with bradycardia pacing can be at risk for developing dysynchrony and deleterious remodeling from RV pacing. Patients provided with ICDs often have cardiomyopathy and/or heart failure (HF). Such patients may exhibit a worsening in their condition such that a Bi-V capable or CRT device may become indicated when it previously was not.
Ultrasound imaging can provide information to assist a physician in evaluating potential dysynchrony conditions, however, use of ultrasound techniques is not universally well understood or available. Electrogram measures, for example QRS width, can also be used as indicators of dysynchrony, however do not provide accurate results in at least certain cases. It will be understood that there is a need for improved systems and methods for identifying onset or worsening dysynchrony conditions, especially in patients who have not previously exhibited significant dysynchronous conditions. It would be further advantageous to provide systems and methods of identifying onset or worsening dysynchrony conditions without requiring additional equipment or clinical diagnostics to increase convenience to the patient and attending clinician while maintaining availability of the improved diagnosis to a wider patient population.